According to increase of energy needs worldwide, a rapid development of mining, especially winning methods can be seen where economy, output increase and protection of health are of basic importance. The method described in the Hungarian Patent 18682 (U.S. Pat. No. 4,626,031) and using the compressed air loosening and breaking coal deals foremost with the protection against methane hazard and includes the steps of:
drilling a bore-hole; PA1 injection of the mineral to be won; PA1 operation of breaking equipment subsequent to its; installation into the bore-hole i.e. loosening and breaking; and PA1 dismounting of the breaking equipment.
From the above mentioned operations injection may not happen if conditions of the mineral to be won do not necessitate it, i.e. there is no need for the extracted mineral for dust reasons.
The winning methods using compressed air having the above mentioned scope of operations are time consuming, circumstantial and have a low productivity, mainly due the fact that winning operations; i.e. drilling, flushing, injecting, instalment and dismounting of the equipment, necessitate a short period of time while the related complicated auxiliary operational steps such as instalment-adjustment and dismounting take long periods of time since these additional operations are subsequent to each other. This is related to the fact that when having a conventional type of compressed air breaking, drilling, injecting and breaking equipment is installed and dismounted one after each other.
For increasing the efficiency of air breaking operations several methods are known. One of them, as described in the Hungarian Patent No. 186 827, has series of compressed air breaking units built into the bore-hole with the self-controlled time-delay equipment and with the outlet openings directed oppositely to the advance direction of the face whereby the compressed air has a concentrated impact in the given direction. Another resolution as described in the Soviet Patent No. 934 915 the downward drilled hole is filled with water and breaking is completed under water by using conventional type of explosives where this uncompressible medium transfers pressure waves of the explosion directly to the coal face thus increasing the efficiency of shotfiring. By having an uphill hole this method cannot be utilized since the question arises as to what way this transmission role of the incompressible liquid can be ensured for increasing of the efficiency of compressed air breaking operation.
There is, however, another problem in the above mentioned technology. Drilling of deep or long holes by using the present drill rod constructions is very difficult especially if straightness has to be also ensured. It is easy to see that by having a bore-hole longer than 4-6 m completed by a 63 mm dia. drill bit, the thin spiral drill rods may partly deviate and/or swing during rotation and therefore the drill bit is not rotated around a straight axis making the hole diameter much bigger than required.
Deviation of the drill rod upon rotating gives the same result when hitting the wall of the bore. The increased diameter and the curved geometry of the bore-hole reduce the working efficiency of the high pressure breaking unit and the length as well.